Composite Decking
If you're reading this, you probably have a wood deck. Maybe your wood deck failed even though you spent countless weekends over the last 20+ years applying the best stains or sealants you could get. Or you paid a contractor to refinish it every other year and it succumbed to the elements anyway. You are tired of the hassle and have promised yourself you will never own another wood deck. If this sounds like you, read on...
Everywhere you look, there are non-wood decking options that promise to last forever with little to no maintenance. All you have to do is keep it clean and it will last 25 years and beyond. Sure, they cost more upfront. But you will save in the long run. No more power washing. No more staining. No sanding. No more headaches. But is it true? Is there really a maintenance free option that lasts?
The emergence of Composite Decking
In 1988, Roger Wittenberg invented a product called Rivenite. Using recycled plastic bags and sawdust, the material was heated, pressed and extruded into deck boards. In 1992, he sold this idea to Mobil Oil. Mobil had limited success in marketing this new material. So, in 1996 Wittenberg bought the idea back and took it public as Trex. Early Trex was marketed as an alternative to wood decking that required no maintenance and would last indefinitely. This proved to be a lofty (and expensive) claim!
The problem with wood plastic composites (WPC)
Many claims have been made about the longevity of WPC compared to natural wood decking, with most WPC claiming to last 25 years or more. Many of the companies making this claim have been in business 5 years or less. The only WPC that's been around long enough to make this claim is Trex (29 years). The other companies making this claim simply do not have the history to back them up. So, how do they know it lasts 25 years? The truth is that they don't. There is a long list of WPC's that have gone out of business. As the warranty claims start to come in they simply cease operations. Then they change the name (and hopefully the product) and start producing under a new name. (ChoiceDek turning into MoistureShield is a great example of this)
The problem with Wood Plastic Composites (WPC)
Warping and Movement
Composite decking companies claim WPC is more stable than wood. This is simply not true. Composite decking is prone to high longitudinal expansion and contraction with seasonal temperature fluctuations and must be installed with large gaps (up to 1/2") at the ends of each board. There is a high amount of movement between winter and summer (especially here in Michigan).
WPC are not considered a structural material and cannot span 16" joist spacing recommendations found on most traditional deck frames. This is because WPC is made up of wood flour (dust) and plastic, not fibers, making it prone to sagging between joists. Most WPC manufacturers now recommend 12" joist spacing to prevent sagging, but it can still sag slightly between joists even at this joist spacing.
Cracking and Breaking
WPC is not immune to cracking or breaking. Because it is a pressed material containing wood dust instead of strands or fibers, it can break near the installation clips or around screws, especially near the ends and edges of the boards.
Mold Issues
Perhaps the biggest issue with WPC is mold growth. Because the wood component is finely ground, all of the wood's natural mold resistance is removed. The wood flour used in WPC is a perfect source of food for mold, mildew and fungal growth. Nearly all WPC producers have followed Trex's lead by cladding the pressed core with a virgin PVC layer on the surface. But the core still gets moldy. The long term effects of this are currently unknown, since this cladding process has only been in use since 2010.
Product Expansion
Most newer WPC is made up of two parts. There is the pressed component in the middle which consists of wood flour and plastic. Then there is the outer layer, which is a plastic shell that encapsulates the core. These 2 components act differently. As the core swells due to moisture content, mold growth, or temperature fluctuations, it can cause the outer layer to separate from the inner core, especially on the edges or cut ends.
Environmental concerns
Most composite manufacturers push the environmentally friendly angle. Combining plastic bags, wood waste, preservatives, dyes, chemical additives and molding it all under high heat doesn't sound very environmentally friendly. WPC products leach oil. And sadly, WPC's are a prime example of a monstrous hybrid--a combination of materials that by themselves are recyclable, but once together can not be separated. WPC decking in its current form will eventually be headed for the local landfill.
Early Trex Decking Problems lead to the Introduction of Trex Transcend in 2010
Trex suffered some dark days in the early years when it was found that the wood flour used in Trex was susceptible to mold, mildew and fungal growth. The boards swelled due to moisture. The colors faded greatly. Expansion and contraction in warm and cold weather caused warping, sagging and even surface flaking. These issues caused millions in warranty claims and Trex eventually settled a class action lawsuit. In 2010, Trex came up with a fix for these earlier problems when they introduced their Transcend line. The "recycled" core is covered on three sides with a protective polymer coating, thereby preventing surface problems. However, the core is still highly susceptible to mold growth. While the surface is much less susceptible to mold growth, the full effects of mold growth in the core are yet to be known.
Since Trex was formed in 1996, there has been an explosion of wood alternatives in the decking industry. Composite decking seems to be trending away from wood as an ingredient due to the mold, mildew and fungal concerns it presents.
This picture shows mold growth in the core of the latest version of PVC capped decking after two years.
This photo is from gardenstructure.com shows an extreme example of what happens to early generation uncapped composite decking when it's installed with the joists too far apart. Most composite deck manufacturers have changed their recommended joist spacing to 12" OC (recommended 16" OC for standard wood decking).
There is an excellent article on the wood vs composite debate by Lawrence Winterburn at gardenstructure.com
Mold, mildew, and fungal issues on the surface of composite decking has caused many producers to go out of business.
Wood flour in composite decking provides the perfect environment for growth to thrive. Fungicides can be used to control growth on the surface of the boards, but it is impossible to completely remove molds from within the boards.
For an older composite deck such as first generation Trex, using a fungicide, power washing and staining with a mildew resistant penetrating oil stain is an effective way to control this problem. However, Trex has been very resistant to proposing this as a fix. And most homeowners are also resistant to this idea. The idea that your composite deck will need ongoing refinishing to mitigate this issue, including the application of a penetrating oil stain. The first reason they chose composite decking was to avoid ongoing maintenance.
Rice Hull Composites
There are some newer companies using rice hulls instead of wood flour in the production process to alleviate the mold issues associated with wood flour (TruNorth, Ontario). Rice hulls are a prevalent food waste byproduct and by themselves do not absorb water. However, there is emerging reasearch that rice hulls don't bond as tightly with the plastic. This creates larger pockets in the material for water to penetrate, and may make them even more susceptible to damage from freeze/thaw cycling. TruNorth's website states they've been in the plastic recycling business for 40 years. Their website doesn't really say when they started producing composite decking, though. Further research shows that they started building their deck plant in 2016 and have been producing decking since 2021. Maybe rice hull instead of wood flour composite decking is the answer. Only time will tell.
For more information on Rice Hull Composites click here
Limestone Composites
Some companies now use ground stone as a substitute for wood flour (Deckorators). As a result, this composite attracts much less mold growth and performs much
A Final Word on Composite Decking
Composite decking has come a long way in 29 years. There are now hundreds of composite decking manufacturers in business. And even more than that have gone out of business. Almost all these manufacturers warranty their products for 25 years, and some are even longer. These warranties are crafted without much real world/real time studies to back up the claims they make. Any warranty is only as good as the ability collect on it when something goes wrong. I have personally heard horror stories of companies blaming improper installation/use as a way to avoid paying claims. And many companies cease operations under their current name, only to reopen under a new name to avoid paying out. Let's face it, a product either works or it doesn't. When it doesn't, there is a good chance that everyone who received the material is going to have a similar experience with it. If there are claims against fading, everyone is probably experiencing fading. If it sags, it will sag for everyone. If the surface flakes, most will experience surface flaking. If it scratches easily, well, you get the idea. The company cannot pay all the claims and stay in business. So they make excuses why the problem occurred or the company goes under. The factory producing the material changes the formula to try and rectify the problem, then keeps producing. Only, now it's under a new name with a "new and improved" material. Composite decking is getting better, no doubt. But using consumers as the test group for the products has become the standard method of evolution in the industry. Then if you can collect on the warranty, what are you going to do with the new boards they drop in your driveway? You still have to have them installed or the old deck removed and the new deck built. The labor required to fix the problem is rarely, if ever, included.
Vinyl decking (wet in the middle of the photo, and dry on the edges)
UV light degrades the plastic and causes oxidation. Certain chemical cleaners and fungicides can make the deck more susceptible to UV damage by removing the oils from the surface of the product.
The fix for this...clean, polish, buff or sand the oxidation off and use a penetrating oil stain. Notice that when it is wet the problem "disappears", an oil stain can have the same effect.
Are you trying to talk me out of using Composite Decking?!
Not really. Well, kind of...maybe. It is important to know that the promise of a product that lasts forever with zero maintenance is a myth. Or better to say, the non-wood options are still a work in progress. As companies go under, new options are constantly emerging. Deck Shine is of the opinion that the non-wood option that includes a realistic ongoing maintenance process as part of the offering will eventually emerge and outperform all of the current composite decking in the industry, and then perhaps outperform natural wood itself. In other words, composite decks will require ongoing maintenance in the future. Eventually, wood probably won't even be an option because it will be cost prohibitive. Natural wood decking will be the more expensive option. In some ways, it's already happening.
Currently, the composites that perform the best are also the most slippery. When new, the surface feels oily to the touch. But over time, the surface oil leach out and dissipate, natural UV exposure will degrade the surface and make it more porous, and the boards will degrade even faster. Rain water is naturally acidic which contributes to this process. So far, I have not personally seen a composite deck that looks good after 10 years. They all substantially degrade within a decade. Then they require ongoing maintenance including the application of a stain or sealant, thus defeating the purpose of installing them in the first place. Soon, composite decking will be the less expensive option. Natural wood will again take over as the preferred (and more expensive) choice.
Perhaps we should be asking...Why did my last deck fail? What could have been done differently that would have made it last indefinitely? A wood deck doesn't rot because it's made of wood, it rots because of the way the deck was constructed!
The most important factor in extending the life of any deck, regardless of the type of decking used, is the way it is constructed. All decks must be framed so that debris will not sit in the joints and all rainwater must be able to drain through at all connection points. For more on this topic, see the Build section.
Cottage deck built by Deck Shine
Product: ChoiceDek
Product was solid composite. I liked that it could be cut, milled and fastened like wood. This allowed us to create the framing around the laminated safety glass panels across the upper railing. This product was originally rated for underwater use (beaches, docks, etc.)
No longer in business. They reinvented themselves as Moisture Shield--using a PVC capped composite core, similar to Trex. Most composites today are using a capped core concept (Trex Transcend).
Contact Deck Shine about your next project. Email Arthur McKinlay at art@deckshine.net or call 248-988-7518